The invention relates to a device for pumping meat-containing products, such as pieces of meat, meat paste and meat pulp (dough), in an essentially uniform stream, having a number of displacers such as pistons, which alternate during the pumping.
Such meat pumps are used to pump the meat to systems where further operations are carried out, for example making sausage, meat metering to all kinds of casings, for example for hams, checking of the meat for, for example, pieces of bone and other characteristics etc.
Meat paste and meat pulp constitute a fairly uniform mass with at most very small cohering original meat particles (in any case less than 1 cm maximum transverse measurement) and can be obtained by grinding or cutting and, for example, from bone presses, in which (remaining) meat with bones is placed under high pressure in order for the meat to be separated from the bones and leave the press through fine holes as a paste.
Devices for pumping meat are known in various designs. For example, rotary vane pumps for meat are known, to which the meat is fed from a feed hopper via a worm screw under vacuum, something which is suitable only for pieces of meat. Meat pulp and meat paste have the tendency to tunnel formation, in other words, meat which is at a standstill for some time, here for example above the worm screw, does not move downwardly very well or not at all, for example into the range of the screw, and thus forms a bridge.
Devices of the type referred to in the preamble, with alternating displacers, have become known, inter alia in order to eliminate the disadvantage of such tunnel formation.
For example, meat pumps are known in which a reciprocating displacer forces a stream of meat product batchwise towards an outlet, at which outlet is connected a second displacer which moves back to allow its delivery space to be filled by the first displacer when the latter is pressing, while the second displacer empties its thus filled delivery space while pressing towards the outlet when the first displacer is moving back. A disc-shaped non-return valve between said delivery spaces makes this possible. The meat is greatly churned up in the process, particularly by the first displacer when it is moving back into the feed space, and in this case some of the meat can easily remain too long in the feed space.
Meat pumps with two parallel reciprocating displacers in the bottom of a feed space are also known, connecting to a common outlet, while at the place where the outlets of the two displacers meet to form a common outlet a reversing valve moving under the influence of the pressure of the meat is provided. In order to ensure that the displacers are capable of forcing the meat towards the outlet under a desired pressure, each displacer has a cylinder which encloses it tightly, and which is also reciprocatable for the purpose of being moved between a retracted position, in which it is retracted from the feed space at the side opposite the outlet, and an extended position, in which it is entirely positioned in the bottom part of the feed space and connects to the appropriate outlet. When each displacer is retracted away from the meat outlet, its cylinder moves with it. On the delivery stroke the cylinder first moves to the extended position, following which the displacer can put pressure on the meat mass taken up therein by the cylinder on that movement, and which is separated from the rest of the feed space, and can force it towards the meat outlet.
The cylinder with sharp front edge makes this system unsuitable for pieces of meat, while the cylinder each time the meat above it at a standstill for so long that the above-mentioned tunnel formation occurs in the case of meat paste and meat pulp, so that it does not sink down again quickly and completely when the cylinder is retracted.
The object of the invention now is to improve this and to provide a device of the type referred to in the preamble, suitable not only for pieces of meat but also for meat paste and meat pulp, in which the above-mentioned disadvantages do not occur, a uniform meat flow through the device and to the outlet can be achieved, and the residence time of all meat in the device is approximately equally short.